4-Tube Elkin Repairs

 This is a 4-Tube Elkin amp a friend picked up at a hamfest. It was in need of a bit of repairs and some updates. The Elkin amps are grid driven, link coupled, push-pull Class Ab2 designs. Very clean spectrally, well made, and were regionally popular on CB in the 60's through the 80's. It was named for the town in was built in, Elkin NC. 

Some of the later mobile models were band switched for 40 through 10m, and the tank in input circuits of the fixed station amps were tapped. I ran a 12-tube version on 40m for many years, with 0 problems. 

Here's a batch of pics, some vids, and descriptions:

A few pics above of the finished amp...

An initial look under the chassis shows a bit of a mess...

The negative voltage pass transistor is literally bridged B to C... smh...

An attempt at screen regulation was also all fubar...

Another transistor was bolted in, collector grounded, and nothing else.

Incorrect tubes installed... One had literally melted the glass and started to implode.

Correct tubes installed, note size difference with the small tubes that it came in with...

Bleeder resistors incorrectly wired, and some were bad.

Filter caps were shot...

Keying circuit for contact closure output was incorrectly wired and kinda hanging in the wind...

Delay cap blown open...

2 Plate caps were broken free of the aluminum tank coil. That stuff has to be soldered with a combination aluminum rod. 

New filter caps in...

New bias regulators installed and wired correctly...

Replacing bias caps...

Plate choke replaced...

Split Plate tune cap needs padding...

Spot drilled and smoothed for variable 150v screen supply...

Dual Filament switch installed to enable use of 6v or 12v tubes...

Variable screen supply installed...

Split input coil adjust and sealed...

Split plate tune cap padded properly...

A number of new parts installed :-)